Blood in contact with an artificial surface can lead to short term platelet deposition, activation and thrombosis, and to coagulation via activation of the intrinsic clotting system. Long term effects may result in complement activation. This proposal centers on utilizing a new class of PEO molecules, in the form of stars, to accomplish two things: (1) Completely cover the underlying support material so that it cannot be accessed by any of the precursors of thrombosis, coagulation or complement activation. This should produce a "non-thrombogenic" surface, but not an "anti-thrombogenic" surface. (2) To provide at the same time molecular "leashes" (i.e., PEO chains), at the ends of which are covalently attached a molecular such as heparin which will carry out a specific interaction with blood. This is an example of a (potentially) antithrombogenic surface.